Attribution effects

Currencies
Naturally this is the first order effect and captures the extent to which the portfolio’s currency exposure outperforms the currency return of the benchmark. The currency returns incorporate both fx changes and short term interest rates. All other effects are then on a fully hedged basis to remove any double counting of currency effects.
Credit
This shows the extent to which the portfolio’s relative exposure to various credit ratings affects its performance. The calculation strips out any duration related effects, and also takes into account the extent of the deviation from AAA rated bonds.
Duration
Duration effect captures the impact of parallel changes in yield curves. The effect depends on the extent of any such move, and the extent to which the average duration of the portfolio is different to that of the benchmark.
Twist and butterfly
Twist captures the effect of any changes to the slope of the curve, whereas butterfly shows the effects of changes in curvature of the yield curve.  Both effects are based on the Nelson-Siegel optimization technique.
Other
The yield effect simply captures the performance impact of the passage of time, and is separate from other effects. It is also known as the carry effect
The country effect results from different countries having different yield curves. 
The stock specific effects are the remaining effects as they apply to each individual security.